Supply and Fuel Properties
Fuel properties you must know
- Kerosene (28-second oil) - the standard domestic heating oil. Low sulphur, clean burning, suitable for pressure-jet burners.
- Gas oil (35-second oil) - heavier, used in some larger or older appliances and commercial plant.
- Flash point, viscosity, calorific value, sulphur content, cloud point and pour point, and waxing behaviour at low temperature.
- Specific gravity and why it matters for gauging and for detecting contamination.
The supply system
- Gravity feed from a tank above the burner, versus two-pipe (sub-gravity) supply with a lift and a return.
- Top outlet with a dip pipe versus bottom outlet, and the role of the fire valve and filter.
- Pipe sizing depends on flow rate, length, lift and fittings; undersized pipe causes pump cavitation and erratic running.
- De-aeration: two-pipe systems return air and excess oil to the tank; single-pipe systems rely on bleeds.
- Filters and water traps protect the nozzle and pump; water in oil causes flame failure and corrosion.
Traps in questions
- Mixing up the two oil grades by their second (viscosity) number.
- Forgetting that a lift reduces available pump suction and may require a two-pipe arrangement.
- Assuming any pipe diameter will do - length and fittings count.
- Overlooking that air leaks on the suction side cause the same symptoms as a blocked filter.
Worked example
A burner runs and then locks out after a few minutes, with a clear filter and good tank level. Rule of thumb: suspect air on the suction line before condemning the pump. Check joints, the fire valve and the dip pipe connection; air ingress shows as a frothy sight-glass or repeated bleeds.